"When you meet someone, they're sizing you up on two fundamental qualities: strength and warmth," says Kohut, a founding partner of Washington, D.C.-based KNP Communications, which specializes in preparing public figures for speaking events. "Strength measures how much people can affect the world, and warmth shows how much people are concerned about our interests."

Kohut and Neffinger came to this conclusion after years of seeing the same issues in their clients' body language crop up. Most seemed either timid and uncomfortable (lacking strength) or confident but cold (lacking warmth). The rare star, the kind of person who's "got it" — that magical thing called charisma — managed to project strength and warmth simultaneously.

This insight has implications for people at all levels of their careers, Kohut says, since being identified as having leadership potential requires that you seem both competent and likable. "When we think about the people we want as leaders, we need to respect their ability, and we need to like them to want to follow them," he says.

The trouble is it's extremely difficult, if not impossible, to portray both at once. Acting in a way that makes you seem strong, whether puffing your chest or using big words, may show your capability but can be off-putting, says Kohut. And when people display warmth, by doing others favors or agreeing with others' viewpoints, they give away their strength. "The balance is hard to strike," he says. In fact, he believes those who've mastered it are merely multitasking, switching between tasks so swiftly it seems fluid.

What's more, physical qualities that are out of your control can automatically influence others' perceptions of you, Kohut says. Having a smaller frame may reduce your strength, for example, but having an attractive face may increase your warmth. By the same token, women are typically perceived as having more warmth and less strength, whereas the reverse is true for men.

Yet when women move to exert their strength, particularly in professional settings, they are often penalized for going against type and are no longer viewed as warm, but instead as "cold" or "bitchy." Says Kohut, "This is the uneven playing field. Women have to actively dial up both warmth and strength." As Facebook COO Sheryl Sandberg writes in her bestselling advice book "Lean In," to get ahead women must be confident, fierce negotiators, and oh so nice.

So how can you find the balance and become more compelling? "The easiest and most common thing that all of us can do is stand up straight and smile," says Kohut. "It sounds basic, but it's really important."

Body language and verbal cues play a huge part in reflecting both qualities, he says. If you want to dial up strength, good posture, eye contact, and confident articulation will make you seem powerful. You can also watch the body language of others to see how they're responding to you, Kohut says. When someone backs away or leans out of a conversation, you may be coming on too strong.

If you want to dial up warmth, smile, lean in to conversations, and mirror the feelings and gestures of others to appear empathetic. You could also establish common ground by complimenting a project they worked on or agreeing with their perspective. "When you agree with people, you're confirming their view of the world," says Kohut. "Then you seem more familiar."

If you're unsure of which quality you may be lacking (or overdoing), he suggests asking a trusted friend or video-taping yourself giving a presentation, so that you can clearly see yourself.

"When you discover the lens of strength and warmth," Kohut says, "it changes the way you see yourself and the world."